Any thoughts on whether it is possible for a hypothermia-prone person to do this race safely in March (instead of the usual June) if air temps are in low 50s (if we're lucky)? Not so much worried about the swim as the aftermath in chilly temps. Have done San Fran Tri at Treasure Island in November and one foot didn't thaw till half way through the run. And I wore full wetsuit, booties, neoprene cap. Any warming strategies? Bag it till next year?

People who do long distance swims would coat themselves in a really thick layer of Vasaline. That a good trick to try on all expose areas, including the feet that is inside the booties. Surfers sometime would bring a warm mug with them and pour it into their wetsuits before going out in the waters. On the bike, you can also wear booties to protect against the wind and the cold.

Why don't you head out to Sandy Point and try out those tricks to see if they would work for you. Sandy Point's water temp in October/November would be similar to SF Bay in March. I read somewhere where the water temp in SF Bay in March isn't that much different than June.

I once swam in the IM Cali 70.3 in Oceanside one year where the water temp was mid 50s. A swim cap over a neoprene cap kept me pretty warm. If you are that afraid of the cold, swim cap over neoprene cap over swim cap :)